The sporogonic development of the parasite in the vector mosquito is a weak link in the course of malaria transmission from one human to another. If the development is interrupted, the transmission of malaria is blocked. Interference with this development in vector mosquitoes is, therefore, a rational strategy to block the spread of malaria. To design such strategies, however, an understanding of the biology of the parasite development in the vector mosquitoes is essential. The development of malaria parasites in the mosquito is elaborate. After being ingested by a mosquito, the parasite undergoes complex changes that occur in stages. These include development from gamete to zygote, transformation from zygote to ookinete, and development from ookinete to oocyst. Within the oocyst, the parasite multiplies into numerous sporozoites, which are infectious to humans. To understand the biology of malaria transmission all of the following need consideration. 1) It is important to understand the biology of the parasite development in mosquitoes, such as signaling pathways that controls parasite transformation from one stage to another. 2) One also needs to know the structural and biochemical properties of the mosquito tissues that the parasites must interact with for further development. 3) It is also essential to study the molecular, cellular and physical aspects of the parasite-mosquito interaction and 4) more importantly it is crucial to investigate how the parasite evades the insect immune system that is so potent in killing inoculated bacteria and fungi. We therefore investigate 1) the developmental changes that occur in the mosquito stages of the parasite, 2) the interaction of parasite with the mosquito midgut, and 3) the mosquito response to the invaded parasite.